Porcelain tooth-crown and backing adjustment.



F. E. HART.

PORCELAIN TOOTH CROWN AND BACKING ADJUSTMENT.

APPLICATION FILED MAY 10, 1915.

Patented Jan. 15, 1918.

T net M24 FFEQ.

FRED E. HART, OF SAN FRANCISCO, CALIFORNIA.

PORCELAIN TOOTH-CROWN AND BACKING ADJUSTMENT.

Specification of Letters Patent.

Patented J an. 15, 1918.

Application filed May 10, 1915. Serial No. 27,201.

reinforced by gold or suitable metal and by means of which it may be secured to the root of a natural tooth or to the supporting member of a bridge, etc.

One of the purposes of my invention is to provide a porcelain crown structure which may be readily removed from its support or backing during the process of construction and during the operation of soldering orcasting the solid metal backing to the backing sheet which conforms to the rear side of the porcelain member so that the latter may not be subjected to the intense heat which would endanger its integrity; and to a construction by which it is easy to replace broken teeth without removal from place of the metal backing; and to a construction by which porcelain teeth or crowns can be secured to bridge plates when the latter are fixed in the mouth. Another object of my invention is to provide a construction which will oifer great resistance to the stresses and pressures to which the teeth are subjected during the process of mastication. Other objects will be apparent from the following description taken in connection with the accompanying drawings, in which Figures 1 and 2 are side elevation and vertical section respectively of a porcelain member of a crown adapted for an anterior tooth such as an incisor or cuspid; Fig. 3

is a side elevation of my supporting post and attached backing sheet; Fig. 4 shows the manner in which the backing sheet is bent in order to conform to the configuration of the rear side of the tooth; Fig. 5 is a vertical section of the tooth shown in Figs. 1 and 2 with the supporting post and sheet metal backing in position; Fig. 6 is a vertical section of a porcelain member of a crown adapted for a bicuspid or molar tooth; Fig. 7 illustrates the manner in which the backing sheet is bent with relation to the supporting post of such a tooth; Fig. 8 shows the backing of Fig. 7 in a proper position on the porcelain member shown in Fig. 6; Fig. 9 shows the manner in which the metal is cast onto the metal backing and post to form a complete crown; Fig. 10 is a vertical section of a porcelain molar tooth adapted to be soldered or otherwise attached to a bridge.

The stresses to which the teeth are subjected are mainly in a vertical direction and I therefore provide a comparatively large flat surface indicated at a. which is in a substantially horizontal plane when the teeth are in use and therefore perpendicular to the vertical stresses, these being resisted by the solid mass of metal forming the backing of the tooth. Inasmuch as the upper teeth are the ones which are more frequently crowned, the stress to which the porcelain is subjected is more largely upon the lingual surface 6 and in order that this part of the tooth may not be weakened I place the hole 2 and the groove 2 which forms a continuation thereof near the opposite or labial side of the tooth and parallel thereto. The post is also substantially vertical when the teeth are in use and in alinement with the vertical stresses and accordingly are not as great a transverse or shearing stress as they would be if placed at an angle to the longitudinal axis of the tooth. Furthermore it will be observed that by placing the fiat surface a perpendicular to the longitudinal axis of the tooth there is far less tendency to loosen the porcelain member from the metal backing than if this surface were oblique, for in the latter case the normal pressures exerted upon the teeth would tend to slide one portion over the other along the oblique line of juncture. The groove 2 which forms a continuation of the hole 2 extends from the flat surface a where the hole emerges, to the base or gingival end 6 of the tooth, thereby affording a very long bearing surface for the supporting arms 4 4 forming the T-head of the supporting post, the stem 4 of which passes through the backing plate 6. This non-central position of the channel for the supporting post leaves the incisal end 0 and lingual side of the tooth solid and thereby affording the greatest strength.

In fitting the supporting post and backing .sheet to the porcelain member 1, the sheet is first bent at right angles over the stem 1 in the manner indicated in Fig. 4: and in dotted lines in Fig. 3. The T-head of the post is then slipped into the hole and groove in the porcelain member and the lower part of the sheet is bent toward the rear side of the member while the outer edge of the horizontal portion of the sheet is burnished over the edge e which has been previously beveled or ground 01f as indicated in Fig. 1 so that the burnished sheet metal will form a cup thereover to more firmly hold the porcelain and to permit the gold backing which is afterward cast thereto to project over the margin of the porcelain at its greatest diameter, as indicated in dotted lines in Fig. 5 to thereby reinforce and strengthen the tooth at that portion which receives the direct vertical thrust and pressure. The upwardly extending flange 6 of the backing sheet and the solid metal which is cast thereto forms a pocket for the horizontal offset of the porcelain member and cooperates with the arm 4? of the post to resist lateral stresses tending to force the porcelain member away from the backing. This is a very important feature of the structure of the tooth. The T-head of the post comprising the arms 4*, 4 is preferably round in section and the arm 41 is then beveled upon the rear side so that it will conform to the shape of the groove 2* in the porcelain member. It will be observed that this beveled rear side of the post arm 1 bears against the metal backing sheet and is rigidly supported thereby. The stem 4 of the post constitutes a support and reinforcement for that portion of the backing sheet which is bent outwardly at right angles to the longitudinal axis of the tooth. When the metal backing is cast to the backing sheet, as indicated in dotted lines in Figs. 5, 9 and 10, the stem 1 is embedded therein and becomes an integral part thereof, thus forming an exceedingly strong and rigid support for the post which enters the groove and hole in the porcelain member.

Figs. 6, 7 and 8 show my invention as applied to a bicuspid or molar porcelain crown and the construction will be understood from the foregoing description of the preceding figures. It will be noted that the hole 2, which, as previously explained, is non-central being near to the buccal surface and parallel therewith occupies a position in the strongest part of the tooth, being substantially on a central longitudinal axis of the buccal cusp f, thereby leaving the central occlusal or grinding surface of the tooth entirely solid. If this hole 2 for the supporting post were placed in the center of the tooth it would so weaken the tooth that it will be liable to fracture under the stress of mastication, since it will be noted. that in the act of chewing food great stresses are exerted from the center in both directions toward the buccal and lingual cusps.

This construction produces the maximum strength and arranges the several parts of the crown in such a manner that they cooperate to the best advantage in resisting the enormous stresses to which a tooth is subjected. The head of the supporting post passes through the buccal portion of the tooth where there'is greatest bulk and the lingual portion which receives the direct vertical grinding pressures is incased in gold and backed by a solid lump or mass of metal 12 which is suflici'ent to resist any tendency to fracture. Another advantage in locating the supporting post'near the front or buccal surface of the tooth resides in the fact that it can there resist to the best advantage any tendency to dislodgment of the porcelain by sticky foods since these obtain a very slight grasp on the lingual or proximal walls of the tooth and obtain the firmest hold upon the buccal surface which is entirely exposed to its influence; and consequently a post located near the buccal wall affords the best resistance against the pull or stresses afforded by such sticky foods. Such resistance is greatly assisted by the fact thatthe arm 9 of the post extends in a groove near the buccal wall to the base or gingival end I) and this also resists any tendency toward lateral or rotary movement about the stem at.

It is important that there should be a suflicient bulk of metal in the backing to prevent any yielding or vibration under the stress of mastication as this would tend to loosen the porcelain member from the backing. My construction of a porcelain member with an. extended flat horizontal surface a not only affords the proper construction to resist the vertical pressures, but also affords ample room for a large mass of solid metal in the backing and makes the tooth absolutely rigid. In case it is desired to further reinforce the teeth to a long bridge, a stiffening bridge wire 10 of hard metal may be laid across the teeth within the angle of the backing sheet, as indicated in Fig. lObefore the backing metal is cast thereon to connect the adjacent teeth of the bridge.

lVhile I have described in detail the particular construction illustrated in the accompanying drawings for the purpose of fully disclosing an embodiment of my invention, I am aware that various modifications may be made therein without departing from the scope of my claims and within the spirit of my invention.

1 claim:- r V '1. An artificial tooth comprising a porcelain member forming the articulating portion and the facing portion, the rear side of said-member having a flat supporting surface substantially perpendicular to the longitudinal axis of the tooth and a surface extending from said flat surface to the base or gingival end of the tooth substantially parallel with the outer surface of the facing, and having a longitudinal groove terminating in a hole extending from said flat surface into the body of said member, a metal backing sheet bent to conform to said rear surfaces, and a T-shaped supporting post having its lateral stem passing through the sheet parallel with and bearing against said flat surface and adapted to form a support therefor and the oppositely extending arms of the post head being parallel with the axis of the tooth and fitting respectively in said hole and in said groove.

2. An artificial tooth, comprising a plastic member forming the facing and articulating portions of the tooth and having an angularly recessed rear wall formed by surfaces substantially parallel with the facing and with the articulating portion, respectively and a metal backing sheet bent to conform to said rear surfaces, the edge of the sheet portion parallel with the articulating portion being formed into a cupped marginal flange extending over the outer edge of the adjacent porcelain to more firmly retain the porcelain and to cause the metal backing cast thereon to project over the margin of the porcelain substantially at its greatest diameter.

3. An artificial tooth, comprising a plastic member, forming the facing and articulating portions of the tooth and having an angularly recessed rear wall formed by surfaces substantially parallel with the facing and with the surfaces, a metal plate or sheet angularly shaped to fit the wall of said recess and bearing thereagainst, a supporting post having a laterally extending stem passing through the sheet and extending adjacent thereto to form a reinforcement and an arm extending perpendicularly therefrom fitting into a channel in the plastic member, and a metal. backing cast onto said sheet and around said stem and filling said recess.

a. An artificial tooth, comprising a plastic member forming the facing and articulating portions of the tooth and having an angularly recessed rear wall formed by surfaces substantially parallel with the facing and with the articulating portion respectively, said member being provided with a longitudinal recess parallel with the buccal surface, a supporting post extending into said recess, a metal backing sheet bent to conform to said angular rear surfaces and secured to said post, the edge of said metal sheet being flanged over the adjacent margin of the porcelain member, said post and said flange being thus united by the sheet to anchor the porcelain member against transverse stresses in opposite directions.

An artificial tooth, comprising a plastic member forming the facing and articulating portions of the tooth and having an angularly recessed rear wall formed by surfaces substantially parallel with the facing and with the articulating portion respectively, a metal backing sheet bent to conform to said rear surfaces, and a reinforcing bridge member located in the angle of said bent backing sheet and extending transversely upon opposite sides of the tooth and adapted to connect adjacent teeth upon a bridge.

In testimony whereof I aflix my signature in presence of two witnesses.

FRED E. HART.

Witnesses:

GEO. '1. TROWBRIDGE, ELLA L. SMITH.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents,

Washington, D. G. 

